Photographic stripping film



Nov. 10, 1964 J. n. slNcLAlR 3,156,565

PHOTOGRAPHIC STRIFPING FIL Filed sapt. 1s, 1962 United States Patent O3,156,565 PHOTOGRAPHIC STRIPPING FILM James R. Sinclair, MayfieldHeights, Ohio, assgnor, by

mesne assignments, to Minnesota Mining and Manufacturing Company, acorporation of Delaware Filed Sept. 13, 1962, Ser. No. 223,366 9 Claims.(Cl. 96-83) This invention relates to photography and to photographicfilm. In one aspect, this invention relates to an improved photographicstripping film.

In the graphic arts field and particularly in ph-otoengraving andsimilar processes, the conventional ph-otographie stripping filmconstruction comprises a temporary `support of a suitable transparentfilm `base material. One side of the temporary support carries, inorder, a release layer, a membrane, a subbing layer and a photosensitiveemulsion. The release layer permits the membrane bearing thephotosensitive emulsion to be removed from the temporary support at anappropriate time after exposure. The release layer must therefore serveto adhere the membrane to the temporary lsupport sufficiently to preventthe premature displacement of the membrane but must permit the membraneto be readily and cleanly separated from. the temporary support bypeeling, without the use of solvents to alter the physical nature of therelease composition. An anti-halation layer is generally provided on theother side of the temporary support and usually is 'bonded thereto 1bymeans of an intermediate suhstratum. When polystyrene film is employedas the temporary support, 'appropriate adhesion and release propertiesof the respective layers are particularly difficult problems. Moreover,the plurality of layers are undesirable not `only for achieving optimumphotographic results but also for reducing the cost of manufacturing thefilm.

It is therefore an object of this invention to provide an improvedphotographic stripping film.

Another object of this invention is to provide a photographic strippingfilm which can be manufactured at reduced cost compared to theabovementioned conventional stripping films and which can be cleanlystripped or peeled apart mechanically without the need for a solventtreatment.

Still another object of this invention is to provide a photographicstripping hlm having a polystyrene temporary support and a minimum oflayers thereon.

A further object is to provide a photographic stripping film which maybe inspected during processing by both reflected and transmitted lightland which has a greater cllectivc speed than thc abovementionedconventional stripping film.

Other objects and advantages will bc apparent from the followingdescription.

ln accordance with this in-vention the foregoing and other advantagesare achieved by providing a polystyrene tzmporary support, a rcleasablemembrane 4supported thereon and comprising a minor amount of an acrylicpolymer and a major amount of a cellulose ester or cellulose ether, anda photosensitive layer superimposed on the relcasable membrane. In apreferred embodiment a subbing layer is interposed between thercleasable membrane and the photosensitive layer. as illustrated in thefigure, the several layers depicted therein being exaggerated inthickness and the relative thicknesses being not necessarily in correctscale.

ln the most preferred embodiment shown in the figure, temporary supportl comprises a clear polystyrene film, preferably 'biaxially oriented,containing anti-halation pigment or dye uniformly dispersed therein. Theresulting support is translucent rather than opaque and preferablytransmits about 22% to 24% of the incident light, based on a density ofabout 0.64 as determined by a photoelect 3,156,565 Patented Nov. 10,1964 tric densitiometer. Particularly preferred is an orange colored dyeor pigment which permits the thin temporary isupport to transmit thespectrum from a wave length of about 6000 A. to about 8000 A. An orangedye pigment of this type, e.g., cadmium orange, is suiciently absorptiveof the light to which normal stripping film emulsions are sensitive andthus permits the temporary support to serve effectively as ananti-halation layer. When a clear, non-pigmented polystyrene sheet isused -as temporary support, it may be provided on the reverse side fromthe releasable membrane with =a separate anti-halation layer, which can:be firmly attached to the support by a cellulosic gelatin subbing layer'and an anchoring layer containing a major amount of an yacrylate. esterpolymer and a minor amount of a cellulose ester in the manner describedin United States Patent Number 2,972,534.

The releasable membrane 2 must not only adhere to the polystyrenetemporary support l and be readily releasable therefrom but also mustmaintain its integrity as membrane upon release. Because of theserequirements and because of the problems associated with theirattainment in association with polystyrene film, the composition of thereleasable membrane must be maintained within the hereindefined limits.It has lbeen lfound that such `a membrane is provided by a layercontaining from about 10 to about percent by weight of l.an acrylateester polymer and from about to about 90 percent by weight of acellulose ester or a cellulose ether, with from 0 to about 25 weightpercent of a pla'sticizer, such as dibutyl phthalate, if desired. Thepreferred acrylate ester polymers are the 'binary polymers of methyl andethyl acrylate or methacryl'ate. An illustrative acrylate ester polymeris the copolymer of ethyl methacrylate and methyl acrylate, c g.,Acryloid B-72 (Rohm and Haas). Such polymers may be prepared by theeopolymeriz'ation of methyl or ethyl acrylate and methyl or ethylmethacrylate in the presence of an organic peroxide with the applicationof light and heat, as described in United States Patents 1,937,323 and2,123,- 599. Those preferred acrylate copolymers are prepared frommixtures having :from about 10 to about 40 percent of ethyl methacrylateand from about to about 9() percent methyl acrylate. The cellulose etherpolymers are preferably a lower alkyl celluose ether, such 'as methylcellulose and ethyl cellulose. The cellulose ester polymers arepreferably the cellulose esters of aliphatic carboxylic acids havingfrom 2 to 4 car-bon atoms, such as cellulose acetate, cellulosepropionate, cellulose butyrate and the mixed esters thereof, e.g.,cellulose acetate butyrate.

The abovementioned proportion of the acrylate polymers and the cellulosederivative is critical for the production of a releasable membrane whichcan be adhered to the polystyrene temporary support during manufacturewithout intervening adhesive or anchoring layers and without separaterelease layers. The adhesion of the releasable membrane of thisinvention to the polystyrene temporary support is suicient to preventpremature peeling or separation of the film construction duringprocessing and handling. Yet the releasable membrane can lbe cleanlystripped or mechanically peeled away from the polystyrene supportwithout impairment of its integrity as a smooth and dimensionallyuniform support for the photosensitive emulsion carried on its otherside. It is a particular advantage that no special solvents are requiredto soften the membrane for the release step, since the use of solventscan reduce the cleanness of the release and can result in a strippedmembrane of non-uniform thickness and light transmissive properties.When the releasable membrane contains more than about 45 weight percentof the acrylate ester polymers, the desirable release or strip-apartproperties are adversely affected, and the membrane becomes tightlybonded or anchored to the polystyrene support. When the releasablemembrane contains less than about weight percent of the acrylate esterpolymers, the membrane tends to peel away from the polystyrene supportduring manufacture, handling and preliminary processing.

The substratum 3, if needed to adhere the photosensitive layer to thereleasable membrane, preferably comprises a very thin coating ofnitrocellulose and gelatin, although other suitable substrata may beemployed to anchor the photosensitive layer 4 securely to releasablemembrane 2.

The photosensitive layer 4 may be any silver halide gelatin emulsion ofthe type suited for stripping films. Since high contrast and excellentdefinition are generally required, orthochromatic emulsions arefrequently ernployed.

In an illustrative and particularly preferred embodiment, a translucent,cadmium oxide pigmented polystyrene film having a thickness of about0.005 inch and having the color and light transmission properties notedabove is used. Such pigmented polystyrene film is available under thename Lustrex from Plax Corporation. This film base is coated with thefollowing solution (25% solids) to provide the releasable membrane.

Non-volatile: Percent by weight Cellulose acetate butyrate second,Eastman Chemical EAB 381-20) 64 Copolymer of ethyl methacrylate andmethyl acrylate (Acryloid B-72) 16 Dibutyl phthalate 20 Volatile:

Ethyl acetate 3.33 Butyl acetate 11.67 Isobutyl alcohol Toluene 10 Ethylalcohol 50 Although various other solvent systems which do not causeetching or fogging of the temporary support may be employed, thepreferred solvents systems, including the particularly preferred rangesin parentheses, are:

Wt. percent Ethyl, butyl or isopropyl acetate 0-20 (l0-20) Butyl orisobutyl alcohol 0-3 (l0-25) Toluene 0-15 (5-15) Ethyl or isopropylalcohol -80 (40-65) Ethyl cellulose can be substituted for celluloseacetate butyrate in the above formulation.

The membrane, after drying, is coated with the following subbingcomposition:

Parts by Weight Preferred Range Gelatin 3 0. 5-4 Water 2 0. 5-5 Glacialacetic acid.- 6 1-8 Nitrocellulose (S55/2 8 0. 5-10 Acetone 18 5-25Methanol 63 25-75 ping film of this invention can be manufactured atsignificantly lower cost than conventional stripping film. Theelimination of a separate anti-halation layer and its associated subbinglayers further reduces the cost. Moreover, the elimination of additionalcoatings brings the antihalation layer into closer proximity to thephotosensitive layer and improves its effectiveness, particularly thespeed of response, which can be as much as 50% faster than aconventional stripping film having a separate anti-halation coating.Furthermore, when the temporary support is translucent rather thantransparent, the operator may visually inspect the exposed strippingfilm during development or processing by reflected light as well astransmitted light. This is in contrast to paper-backed stripping filmswhich can be visually inspected only by refiected light. Theseadvantages in cost, increased speed and definition are of great benefitto photoengravers and other users of photographic stripping film.

A further advantage of the stripping film construction of this inventionis the added utility of the cleanly stripped temporary support, which isan ideal material for masking in layout and makeup work byphotoengravers. With the pigmented, translucent polystyrene film theabsence of further coatings on the stripped support is an addedadvantage.

Those skilled in the art will appreciate that various changes andmodifications can be made in the preferred forms of the inventiondisclosed herein without departing from the spirit and scope of theinvention.

It is therefore claimed:

1. A stripping film comprising a polystyrene temporary support, areleasable membrane on one side thereof consisting essentially ofbetween about 10 and about 45 weight percent of acrylate ester polymerand between about 55 and about 90 weight percent of a member of thegroup consisting of a lower alkyl cellulose ether and a cellulose esterof an organic carboxylic acid having from two to four carbon atoms, saidmembrane being adhered to said polystyrene support and cleanlystrippable therefrom by mechanical peeling, and a photosensitive silverhalide layer carried by said releasable membrane on the side oppositethe polystyrene support.

2. The stripping film of claim 1 in which an antihalation layer iscarried by the temporary support on the side opposite the releasablemembrane.

3. The stripping' film of claim 1 in which the temporary support is atranslucent polystyrene film incorporating an anti-halation materialtherein.

4. A stripping film comprising a translucent polystyrene temporarysupport incorporating an anti-halation pigment, said temporary supporttransmitting from about 22% to about 24% of light incident thereon andbeing substantially opaque to light having a wave length of less thanabout 6000 A., a releasable membrane on one side thereof consistingessentially of between about 10 and about 45 weight percent of acrylateester polymer and between about 55 and about 90 weight percent of amember of the group consisting of a lower alkyl cellulose ether and acellulose ester of an aliphatic carboxylic acid having from two to fourcarbon atoms, said membrane being adhered to said polystyrene supportand cleanly strippable therefrom by mechanical peeling, and aphotosensitive silver halide layer carried by the releasable membrane onthe side thereof opposite said polystyrene support.

5. A stripping film comprising a translucent polystyrene temporarysupport incorporating an anti-halation pigment, said temporary supporttransmitting from about 22% to about 24% of light incident thereon andbeing substantially opaque to light having a wave length of less thanabout 6000' A., a releasable membrane on one side thereof consistingessentially of between about 10 and about 45 weight percent of acrylateester polymer and between about 55 and about 90 weight percent of amember of the group consisting of a lower alkyl cellulose ether `and acellulose ester of an aliphatic carboxylic acid hav' ing from two tofour carbon atoms, said membrane being adhered to sai-d polystyrenesupport and cleanly strippable therefrom by mechanical peeling, acellulosic-gelatin subbing silver halide layer on said membrane, and aphoto- `sensitive layer carricd by the releasable membrane on the sidethereof opposite said polystyrene support.

6. The stripping film 0f claim 5 in which said releasable membrane alsocontains an organic plasticizer.

7. The stripping lm of claim 5 in which said releasable membranecontains ethyl cellulose.

8. The stripping lm of claim 5 in which said releasable membranecontains cellulose acetate butyrate.

9. The stripping lm of claim 5 in which said releasable membranecontains a copolymer of a lower alkyl acrylate and a lower alkylmethacrylate.

References Cited in the le of this patent UNITED STATES PATENTS UNITED'STATES PATENT OFFICE 'i CERTIFICATE 0F CORRECTION Patent No, 3,156,555November 10, 1,964

James RfSinclaiT it is hereby certified that error appears in the abovenumbered patent'requiring correction and that the Said Letters Patentshould read as corrected below.

Column 5, lines 4 and 5, for "silver halide layer on Ead membrane, and aphotosensitve layer" read layer on said membrane, and a photosenstivesilver halide layer Signed and sealedthis 24th day of August 1965.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner ofPatents

1. A STRIPPING FILM COMPRISING A POLYSTYRENE TEMPORARY SUPPORT, ARELEASABLE MEMBRANE ON ONE SIDE THEREOF CONSISTING ESSENTIALLY OFBETWEEN ABOUT 10 AND ABOUT 45 WEIGHT PERCENT OF ACRYLATE ESTER POLYMERAND BETWEEN ABOUT 55 AND ABOUT 90 WEIGHT PERCENT OF A MEMBER OF THEGROUP CONSISTING OF A LOWER ALKYL CELLULOSE ETHER AND A TWO TO FOURCARBON ATOMS, SAID MEMBRANE BEING ADHERED TO SAID POLYSTYRENE SUPPORTAND CLEANLY STRIPPABLE THEREFROM BY MECHANICAL PEELING, AND APHOTOSENSITIVE SILVER HALIDE LAYER CARRIED BY SAID RELEASAB LE MEMBRANEON THE SIDE OPPOSITE THE POLYSTYRENE SUPPORT.